Known in the past has been an acoustic wave device (surface acoustic wave device, hereinafter simply referred to as a “SAW device”) in which excitation electrodes are formed on a piezoelectric substrate. This SAW device is used as a filter for obtaining a specific frequency by utilizing the feature that an electrical signal and a surface acoustic wave can be converted to each other due to the relationship between the excitation electrodes and the piezoelectric substrate.
In a duplexer which is used for a mobile terminal such as a mobile phone, conventionally a dielectric filter has been mainly used. In recent years, however, a SAW device which has a high performance and can be reduced in size and lightened in weight has begun to be used. A mobile terminal carries a SAW module comprised of a SAW device mounted on a circuit board on which a capacitor etc. are mounted. In the mobile terminal, the SAW module has the role of filtering an electrical signal transmitted and received from an antenna portion into a reception signal and a transmission signal by a duplexer.
In recent years, along with the increasingly smaller size of mobile terminals, lowering the profile of a SAW device has become indispensable. As a structure lowering the profile of a SAW device, for example, a wafer level package (hereinafter, simply referred to as WLP) structure is known (for example, see Japanese Patent Publication No. 2010-56671A). A WLP structure SAW device is structured with a cover having via conductors which are to be electrically connected to excitation electrodes formed on a piezoelectric substrate arranged on the piezoelectric substrate.